You need some form of iteration here, as val (except when called with a function) only works on the first element:
$("input[placeholder]").val($("input[placeholder]").attr("placeholder"));
should be:
$("input[placeholder]").each( function () {
$(this).val( $(this).attr("placeholder") );
});
or
$("input[placeholder]").val(function() {
return $(this).attr("placeholder");
});